refactor: Adds type downcasting helpers for InvalidPoolTransactionError

[PanGan21]

Closes: #14037

Adds type downcasting helpers for InvalidPoolTransactionError.

[emhane]

yes, we want to generalise the impl body too

impl<T: PoolTransaction, E> TransactionValidationOutcome<T, E> { .. }

[mattsse]

hmm,

this error already supports arbitrary errors via

reth/crates/transaction-pool/src/error.rs

Lines 223 to 225 in d3cec5a

	/// Any other error that occurred while inserting/validating that is transaction specific
	#[error(transparent)]
	Other(Box<dyn PoolTransactionError>),

skeptical that it's worth integrating an error type

which I think would need to be added to

reth/crates/transaction-pool/src/pool/mod.rs

Line 132 in d3cec5a

pub struct PoolInner<V, T, S>

[emhane]

rollups want to match on their error variants @mattsse . eventually all components that are customisable at sdk level should have an error associated type for good devx.

[mattsse]

rollups want to match on their error variants

what's a use case for this?

[emhane]

rollups want to match on their error variants

what's a use case for this?

do smthg based on the error variant

[mattsse]

can we add a helper that typechecking the dyn PollError instead, don't think a dedicated type for this is super useful

[emhane]

can we add a helper that typechecking the dyn PollError instead, don't think a dedicated type for this is super useful

sure rollups can work with down casting. though semantically it's nicer for the rollups to wrap l1 errors in a variant, so they can extend it. another place I'm having the same problem rn is PayloadError from alloy. in upcoming op fork there is a need for adding other error variants for failing payload validation. instead of moving this problem to alloy to add an Other variant, it would be nicer if the trait PayloadValidator had an associated type for error.

[PanGan21]

yes, we want to generalise the impl body too

impl<T: PoolTransaction, E> TransactionValidationOutcome<T, E> { .. }

I added this for now.
In case the approach needs to change and add the type checking helper function please let me know :)

[mattsse]

@PanGan21

can we instead make this

reth/crates/transaction-pool/src/error.rs

Line 14 in 440e669

pub trait PoolTransactionError: core::error::Error + Send + Sync {

`: Any``

and add

    #[inline]
    fn as_any(&self) -> &dyn std::any::Any;

to the trait?

[emhane]

lgtm

[mattsse]

actually @PanGan21 we probably don't need the additional Any fn if we require that this trait is 'static

and add these helper functions

#14180

to

reth/crates/transaction-pool/src/error.rs

Line 189 in 04c1d71

pub enum InvalidPoolTransactionError {

[PanGan21]

actually @PanGan21 we probably don't need the additional Any fn if we require that this trait is 'static

and add these helper functions

#14180

to

reth/crates/transaction-pool/src/error.rs

Line 189 in 04c1d71

pub enum InvalidPoolTransactionError {

It seems that adding this:

/// Attempts to downcast the [`InvalidPoolTransactionError::Other`] variant to a concrete type
    pub fn downcast<T: core::error::Error + 'static>(self) -> Result<Box<T>, Self> {
        match self {
            Self::Other(err) => err.downcast().map_err(Self::Other),
            err => Err(err),
        }
    }

would give and error about downcast method not found in Box<dyn PoolTransactionError>. Any idea what is the trick to fix it @mattsse ?

[mattsse]

ah yeah this is an issue with dyn trait and casting because the trait is actually PoolTxError not dyn Error.

there's as_dyn_error, but I think the : Any approach I mentioned above would be better here, because in this case the trait must provide the cast to &Any,

let's start by adding fn is and downcast_ref, see #14180
the actual downcast we can solve later

[codspeed-hq]

CodSpeed Performance Report

Merging #14046 will not alter performance

_{Comparing PanGan21:14037-generic-transaction-validation-outcome (95bb0bf) with main (29e6e5c)}

Summary

✅ 77 untouched benchmarks

[mattsse]

smol naming nit, otherwise lgtm

[mattsse]

Suggested change

	pub fn downcast_other<T: core::error::Error + 'static>(&self) -> Option<&T> {
	pub fn downcast_other_ref<T: core::error::Error + 'static>(&self) -> Option<&T> {

[mattsse]

messed up naming on the other pr

[PanGan21]

Done, trying to fix one last issue in is_other, probably related to casting which i discovered from the unit tests

[PanGan21]

Hi @mattsse . It seems that downcasting doesn't work as expected due to rust casting rules. Essentially as you said dyn PoolTransactionError is recognized as core::error::Error + Send + Sync + 'static from err.is::<T>.
Any suggestion that this can be improved?

[mattsse]

what we can do is add an fn as_err(&self) &dyn Error to the trait function itself and impl is just self, this way the type is responsible for the cast
can also be Any instead of Error

like

fn as_err(&self) -> &dyn Error {
        self
    }

[PanGan21]

It seems Any did the trick, thanks!